Well, I would never comment on another authorized vendor's product offering (at least, now that I'm an authorized vendor and am supposed to maintain some semblance of decorum : )

The CAL25 is the Rainbow 25mm tweeter, and the 210.25 SL is the Sound Line 2-way 10cm midrange 20mm tweeter kit. It's become popular because it fits, it's less than the Morels, and it sounds darned good in my opinion. Cast 4" frame, paper cone, silk tweeter diaphragm, and a somewhat large and ungainly but very advanced passive crossover. I mean that it has great parts and also great flexibility - tweeter attenuation, midrange LP slope, notch filter on off, and tweeter polarity. I should test it someday actively biamped off an MS-8 without the passive crossover

We sell the 210.25 at $295 in systems with the rings for the BMW door mid and machining the plastic housing of the tweeter so it snaps into the BMW mount (it is a hair too big to snap in - there are other ways to install it, modding the mount or glue or the like, but we've settled on machining the housing as the best path).